Optimising sample volume and replicates using the Bou-Rouch method for the rapid assessment of hyporheic fauna

Despite the widespread use of the Bou-Rouch method in obtaining hyporheic samples in ecological studies, problems persist in comparing data because of differences in volume and number of samples taken in various studies. Towards standardising this method, we conducted a study in the Delour River, Ireland, between March and September 2006. The hyporheic habitat was divided into three lateral zones: the flowing stream (SS); the stream-terrestrial ecotone (EC); and the terrestrial margin (TM). Between 3 and 6 random insertions of the stand pipe were made into the hyporheic habitat at 0.2m and 0.5m in each zone. Ten consecutive 1-L samples were pumped at each point to determine an optimum sample volume and replicates needed to estimate taxon richness and abundance. The optimum sample combinations range between 6 and 15 3- to 10-L samples depending on depth and habitat zone. Our results show that both spatial and temporal scales are important factors in considering the optimum combinations of sample volume and number of independent spatial replicates needed to sample stream hyporheos, with the zone closer to the flowing stream requiring many small-volume samples whereas areas further away towards the alluvial groundwater need larger volumes with small numbers of replicates.